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A device with the parent $^{229}$Th source was constructed to search for variations of the daughter $^{213}$Po half-life ($T_{1/2} = 4.2$ $mu$s). A solar-daily variation with amplitude $A_{So}=(5.3 pm 1.1) times 10^{-4}$, a lunar-daily variation with amplitude $A_L = (4.8 pm 2.1) times 10^{-4}$, and a sidereal-daily variation with amplitude $A_S = (4.2 pm 1.7) times 10^{-4}$ were found upon proceeding the data series over a 622-day interval (from July 2015 to March 2017). The $^{213}$Po half-life mean value is found to be $T_{1/2} = 3.705 pm 0.001$ $mu$s. The obtained half-life is in good agreement with some of the literature values obtained with great accuracy.
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Results of a comparative analysis of the $^{214}$Po ($T_{1/2}= 163.47pm0.03$ $mu$s), $^{213}$Po ($T_{1/2}=3.705 pm 0.001$ $mu$s) and $^{212}$Po ($T_{1/2}=294.09pm0.07$ ns) half-life annular variation parameters are presented. It is shown that two independent sequential sets of the $^{214}$Po $tau$-values $(tauequiv T_{1/2})$ obtained in the spaced laboratories can be described by sinusoidal functions. The sinusoid curve with amplitude $A=(5.0 pm1.5) cdot 10^{-4}$, period $omega=(365pm 8)$ days, and phase $phi=(170 pm 7)$ days approximates the set of $^{214}$Po $tau$ values obtained at BNO INR RAS during the $sim$973 days starting on January 4, 2012. The function approximates a set of $tau$-values with a time duration of $sim1460$ days obtained at the KhNU has an amplitude $A=(4.9pm1.8)cdot10^{-4}$, a period $omega= (377pm13)$ days and a phase $phi=(77pm10)$ days. The $^{213}$Po $tau$-value set with a time duration of $sim1700$ days can be described by a sinusoidal function with an amplitude $A=(3.9pm1.2)cdot10^{-4}$, a period $omega= (370pm13)$ days and a phase $phi=(130pm9)$ days. The $^{212}$Po $tau$-value set with a time duration of $sim670$ days can be described by a sinusoidal function with an amplitude $A=(7.5pm1.6)cdot10^{-4}$, a period $omega= (375pm13)$ days and a phase $phi=(40pm10)$ days.
The half-life of $^{212}$Po was measured with the highest up-to-date accuracy as $T_{1/2}=295.1(4)$ ns by using thorium-loaded liquid scintillator.
Precise measurement of half-life of $^{212}$Po (one of the daughter nuclides in radioactive chain of $^{232}$Th) was realized by means of liquid scintillator based on toluene doped by complex of thorium and trioctylphosphine oxide with concentration of Th $sim0.1$ mass %. Fast photomultiplier tube and high frequency oscilloscope were used to acquire the scintillation signals waveforms. The algorithms were developed to find pairs of $^{212}$Bi beta-decays and subsequent $^{212}$Po alpha-decays, to calculate time differences between the events in the pair, and to build $^{212}$Bi beta-decay and $^{212}$Po alpha-decay energy spectra. Preliminary the $^{212}$Po half-life is $T_{1/2} = (294.8 pm 1.9)$ ns. The experiment is in progress aiming at reduction of the statistical and systematic uncertainties.
Rare event physics demands very detailed background control, high-performance detectors, and custom analysis strategies. Cryogenic calorimeters combine all these ingredients very effectively, representing a promising tool for next-generation experiments. CUPID-0 is one of the most advanced examples of such a technique, having demonstrated its potential with several results obtained with limited exposure. In this paper, we present a further application. Exploiting the analysis of delayed coincidence, we can identify the signals caused by the $^{220}$Rn-$^{216}$Po decay sequence on an event-by-event basis. The analysis of these events allows us to extract the time differences between the two decays, leading to a new evaluation of $^{216}$ half-life, estimated as (143.3 $pm$ 2.8) ms.
Background: The influence of shell effect on the dynamics of the fusion fission process and its evolution with excitation energy in the pre-actinide Hg-Pb region in general is a matter of intense research in recent years. In particular, a strong ambiguity remains for the neutron shell closed $^{210}$Po nucleus regarding the role of shell effect in fission around $approx$ 30 - 40 MeV of excitation energy. Purpose: We have measured the fission fragment mass distribution of $^{210}$Po populated using fusion of $^{4}$He + $^{206}$Pb at different excitation energies and compare the result with recent theoretical predictions as well as with our previous measurement for the same nucleus populated through a different entrance channel. Mass distribution in the fission of the neighbouring nuclei $^{213}$At is also studied for comparison. Methods: Two large area Multi-wire Proportional Counters (MWPC) were used for complete kinematical measurement of the coincident fission fragments. The time of flight differences of the coincident fission fragments were used to directly extract the fission fragment mass distributions. Results: The measured fragment mass distribution for the reactions $^{4}$He + $^{206}$Pb and $^{4}$He + $^{209}$Bi were symmetric and the width of the mass distributions were found to increase monotonically with excitation energy above 36.7 MeV and 32.9 MeV, respectively, indicating the absence of shell effects at the saddle. However, in the fission of $^{210}$Po, we find minor deviation from symmetric mass distributions at the lowest excitation energy (30.8 MeV). Conclusion: Persistence of shell effect in fission fragment mass distribution of $^{210}$Po was observed at the excitation energy $approx$ 31 MeV as predicted by the theory; at higher excitation energy, however, the present study reaffirms the absence of any shell correction in the fission of $^{210}$Po.
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